Re: [PATCH] KVM: x86: should release vcpu when closing vcpu fd

[Gleb Natapov <gleb@redhat.com>]

On Wed, Aug 28, 2013 at 04:08:10PM +0800, Chen Fan wrote:
> If we want to remove a vcpu from vm, we should not be only to
> put kvm, we need to decrease online vcpus and free struct kvm_vcpu
> when closing a vcpu file descriptor.
> 
It much more complicated that what you do here. kvm->vcpus[] is accessed
without locking and kvm->online_vcpus is assumed to be greater than max
occupied index in kvm->vcpus[]. Attempt where made to make it possible
to destroy individual vcpus separately from destroying VM before, but
they were unsuccessful thus far.

> Signed-off-by: Chen Fan <chen.fan.fnst@cn.fujitsu.com>
> ---
>  arch/x86/kvm/x86.c       | 14 ++++++++++++++
>  include/linux/kvm_host.h |  1 +
>  virt/kvm/kvm_main.c      |  4 +++-
>  3 files changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index d21bce5..3370de1 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6904,6 +6904,20 @@ static void kvm_free_vcpus(struct kvm *kvm)
>  	mutex_unlock(&kvm->lock);
>  }
>  
> +void kvm_arch_vcpu_release(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm *kvm = vcpu->kvm;
> +
> +	mutex_lock(&kvm->lock);
> +	atomic_dec(&kvm->online_vcpus);
> +	kvm->vcpus[atomic_read(&kvm->online_vcpus)] = NULL;
> +	mutex_unlock(&kvm->lock);
> +
> +	kvm_clear_async_pf_completion_queue(vcpu);
> +	kvm_unload_vcpu_mmu(vcpu);
> +	kvm_arch_vcpu_free(vcpu);
> +}
> +
>  void kvm_arch_sync_events(struct kvm *kvm)
>  {
>  	kvm_free_all_assigned_devices(kvm);
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index a63d83e..e0811f97 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -631,6 +631,7 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, unsigned int id);
>  int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu);
>  int kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu);
>  void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu);
> +void kvm_arch_vcpu_release(struct kvm_vcpu *vcpu);
>  
>  int kvm_arch_hardware_enable(void *garbage);
>  void kvm_arch_hardware_disable(void *garbage);
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 1580dd4..442014b 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1873,8 +1873,10 @@ static int kvm_vcpu_mmap(struct file *file, struct vm_area_struct *vma)
>  static int kvm_vcpu_release(struct inode *inode, struct file *filp)
>  {
>  	struct kvm_vcpu *vcpu = filp->private_data;
> +	struct kvm *kvm = vcpu->kvm;
>  
> -	kvm_put_kvm(vcpu->kvm);
> +	kvm_arch_vcpu_release(vcpu);
> +	kvm_put_kvm(kvm);
>  	return 0;
>  }
>  
> -- 
> 1.8.1.4
> 
> --
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--
			Gleb.